This invention is related generally to the quantification of properties in high pressure die cast (HPDC) aluminum alloy components, and particularly to a way to determine material properties in such cast components by taking into consideration both skin and core properties.
HPDC (also referred to as die casting) is being used extensively in the production of lightweight aluminum alloy components in general, and particularly for automotive components, such as engine blocks and transmission cases, as well as pistons or suspension parts. Low costs for large-scale production, close dimensional tolerances (near-net-shape) and smooth surface finishes are all positive attributes that make HPDC so attractive. Unlike alloys (such as 319 or 356) that are not typically used in HPDC, certain aluminum alloys, such as 380, 383, 390 or the like, are particularly well-suited to HPDC for their cost, strength, fluidity and generally good corrosion resistance qualities.
Die casting components generally form an outer skin region or layer that surrounds an internal core region or layer. In general, the material properties associated with the skin tend to be superior to those in the core, where the skin region has an abundance of relatively defect-free, dense microstructure while the core region has a higher concentration of voids, porosity and related defects. Testing for commonly-used figures of merit has shown that the skin region of a cast aluminum alloy component may exhibit up to 15% higher tensile strengths and over 80% more ductility that the core region. In typical cast components, the skin can be between about 100 microns and a couple of millimeters thick, depending on the size and geometry of the component.
In practice, it is difficult to characterize the properties of the skin separately from those of the core. This in turn negatively impacts the ability of the component designer to optimize the design for efficient and reliable operation, where the use of analytical tools (such as finite element techniques) of HPDC components often eschews the location-specific nature of the mechanical properties in favor of assuming the presence of uniform microstructure and properties across the entirety of the cast component.
One approach to more accurately determine the skin layer thickness for a given component is discussed in co-pending U.S. patent application Ser. No. 14/253,119 that was filed on Apr. 5, 2014 and owned by the Assignee of the present application and incorporated in its entirety by reference. The approach discussed therein uses a metallographic technique that takes advantage of changes in the volume fraction of eutectic phases in general, and more particularly where cooling and diffusion dynamics act as a way to help determine where this change occurs. As with all metallographic techniques, it relies upon sensed images (such as those made with a microscope or other magnification device, where the surface of the component being sensed has been prepared to better highlight the microstructural features that may help delineate where different material properties (such as those between the aforementioned core and skin regions) may be present. While such an approach offers significant improvements in determining skin layer thickness, there still remains a need to have a more automated way to correlate the skin layer thickness to a local wall thickness for a given component to automate the determination of skin layer thickness in HPDC components so that metallographic or related additional data-gathering techniques are not required.